Rheostat



March 6, 1934.

H. A. FOOTHORAP RHEOSTAT Filed May 29, 1930 am. t

Patented Mar. 6, 1934 UNITED STATES RHEOSTAT Harry A. Foothorap,Harrisburg, Pa., assignor to Elliott-Fisher Company, New York;N; Y., acorporation of Delaware Application May 29, 1930, Serial No. 457,036

1 Claim.

My invenion relates to electrical resistance devices and moreparticularly to improvements in rheostats for interposing variableresistance in a circuit to control for instance the speed of a 5 motor.

The principal object of my invention is to provide a rheostat which maybe accurately regulated and set to predetermine the speed of a motor andwhich when so regulated or set is proof 1 against accidental orunauthorized change.

Another and salient object of my invention is to provide a small lightrheostat for use in any capacity in which economy in weight and space isessential, for instance in a motor driven typewriter carriage toregulate the speed thereof.

To the accomplishment of the above, and other objects, presentlyapparent, there has been illustrated in the accompanying drawing apreferred embodiment of my invention which will be set forth in detailin the following description and particularly defined in the claimsappended thereto.

In said drawing,

Figure 1 is a view in transverse section of a rheostat constructedaccording to my invention,

Figure 2 is a view in front elevation with the cover plate removed anddrawn to a reduced scale,

igure 3 is a sectional view taken on the line 30 3-3 of Figure 1 andalso drawn on a reduced scale,

Figure 4 is a fragmentary sectional view taken on the line 44 of Figure3 and drawn on an enlarged scale,

Figure 5 is a similar the line 4-4 of Figure 3.

Referring now to my novel rheostat, 8 is the casing thereof constructedof light metal, in the form of a cylinder open at its front and provided40 with an integral back plate 9 having an inwardly extending concentricshoulder 10.

Within the casing 8 is a cylindrical support 12 of insulating materialfor mounting the resistance element presently described. The support 512 is open at its rear side and provided with an axial hub member 13,and a radial flange 14 at its rear edge for a purpose presentlyapparent. Mounted upon the front of the support 12 is a radial L shapedconductor bar 15 (Figs. 3 and 4) 50 having a hub portion 16 locatedaxially of the hub member 13 and secured to the face of the support 12by a plug 17, projecting through a suitable opening 17' in the casing 8.Screws, one of which is shown at 18, passing through the back 55 plate9, and through suitable bosses, one of which 3 sectional view taken onis shown at 19 (Fig. 1) on the support 12, secure said support to theplate 8, the inner edge of said support 12 seating on the shoulder 10whereby it is centered in the casing. The support 12 is narrower thanthe casing 8 to providea space 0 20 between its front edge and the frontend of the casing for a purpose presently apparent.

The resistance element comprises a coil of wire 21 closely wound arounda flat core 22, in this instance a flat strip of insulating material,and :5 partially surrounding the support 12 with its ends terminatingadjacent each side of the conductor bar 15, its front edge overhangingthe front end of the support and its rear edge insulated from the casingby the flange 14. The opposite ends 7 of the core 22 are secured to thesupport 12 by binding posts 23 and 24, (Figs. 1 and 3) respectively,post 23 having the form of a plug socket (see Fig. 5) to which accessmay be had through a suitably disposed opening 25 in the 7 periphery ofthe casing 8. The ends of the coil 21 are connected to said bindingposts, as will be understood.

A sleeve 26 is rotatably mounted in the hub members 13 and 16. The frontend of the sleeve 5 26 projects across the space 20 and has securedthereon, by means of a pin 27, a collar 28, the outer end of which isformed with step shoulders 29 and 30, respectively. A resilient contactmember in the form of a radial arm 31 is mounted a on the shoulder torotate with the sleeve 26 and collar 28 and wipe over the outer edge ofthe coil 21. The current is thus conducted from the coil 21 to thecollar 28 from whence it passes to the conductor bar 15 by means of abowed spring washer 32 disposed on the sleeve 26 intermediate saidcollar 28 and the hub 16 of said bar.

A circular dial plate 33 is suitably fixed upon the shoulder 29, as bythe collar 34, to rotate with the sleeve 26 and spaced from the arm 31by a spacing washer 35. The dial plate is suitably graduated to indicatein ohms, through an aperture in a cover plate 38, the resistance set upin a circuit by different sections of the coil 21 engaged by the contactarm 31.

In front of the dial plate 33 a spider bracket 36 is suitably secured inthe casing 8, as by screws 37. The cover plate 38, which closes the openfront end of the casing, is attached to the bracket as by screws 39,(Fig. 2). The bracket 36 and cover plate 38 are provided with alignedsight openings 40 and 41, respectively.

Secured within the sleeve 26, as by the pin 27,

is a spindle 42 having a rear end portion of small- 1 1o er diameterthan the inside of the sleeve and adapted to receive a suitablyinsulated tubular key 43 which may be inserted through a keyhole 44located in the back plate 9 of the casing. The spindle 42 has awedge-shaped intermediate portion 45, whereby the end of the key may becaused to frictionally engage said spindle so that the sleeve 26 andparts carried thereby may be turned to the desired setting and the keythen withdrawn.

Suitably located stop lugs 46' are provided on the support 12 to limitmovement of the contact arm 31. A collar 47 is removably mounted uponthe rear end or the sleeve 26 as by the set screw 48 so that said sleevemay be adjusted longitudinally to regulate the tension exerted by thecon tact arm 31 and washer 32 to secure ease of operation together withperfect contact and to take up wear on the parts.

The manner or connecting the rheostat in a circuit is immaterial to thepresent invention. but it will oi course be understood that theconnection is made to the plug 17 and the socket 23.

What I claim is:

In a rheostat, a closed casing, a resistance element therein, a sleeverotatable from within the casing only and having a relatively smallerpilot spindle therein for rotating the same. a contact rotated by saidsleeve and cooperating with the resistance element, and a tubular toolinsertible at will from outside the easing into the sleeve and over thepilot spindle.

HARRY A. FOOTHORAP.

